This invention relates generally to a passive damping mechanism for structural vibration control and particularly to vibration control in structure used in aerospace applications.
The control of dynamic vibrations is critical to the operational success of several types of systems. This is particularly true for aerospace systems in which problems resulting from vibrations are prevalent. For obvious reasons, space structures must be made to be as light as possible (it is estimated that each pound of launch weight increases the cost of the launch by about $25,000). These lightweight space structures are highly flexible and in general are characterized by low stiffness-to-mass ratios. This results in a cluster of many low frequency, lightly-damped vibration modes. In a large space structure such as a satellite, the primary mission is usually to gather, transmit and/or receive information from the ground, space or other deployed satellites. This is accomplished with precision measuring instruments mounted on the payload mounting platform of the satellite. Mission goals dictate stringent pointing requirements for the measuring instruments. Thus, the dynamic stability of these instruments is extremely important. Ensuring the required stability is a complex task given the level of vibrations typically encountered.
Both passive damping and active control systems have been used in space structures to meet the dynamic performance requirements. Passive damping typically involves either the modification of key structural design parameters which affect the structural mass, stiffness and damping characteristics or the use of special energy absorbing materials such as viscoelastic materials. Thus, passive damping does not have the power requirements of active control systems and typically adds less weight. A known approach for using viscoelastic materials to dampen vibrations has been to strategically apply strips of viscoelastic material on the platform with a stiff constraining layer to induce shear in the viscoelastic material. However, the incorporation of viscoelastic material in a weight effective manner and the specific positioning of the viscoelastic strips on the platform present difficult design challenges. Furthermore, the positioning of the viscoelastic strips limits the locations on the platform where measuring instruments can be mounted. These issues illustrate some of the complexities faced in vibration control of aerospace structures.